1. Field of the Invention
The present invention relates to a nickel-metal hydride rechargeable battery, and more particularly to a nickel-metal hydride rechargeable battery intended for prolonged life.
2. Description of Related Art
A nickel-metal hydride rechargeable battery including positive electrode plates having nickel hydroxide as its active material, negative electrode plates having hydrogen-absorption alloy, and separators interposed therebetween, has been known and widely used.
In such a nickel-metal hydride rechargeable battery, operations are usually organized so as to have 10-80% of working load range for hydrogen-absorption capacity of the hydrogen-absorption alloy, corresponding to 0-100% of working load range for positive electrode capacity, and that, out of the hydrogen-absorption capacity, around 0-10% is set for a discharge reserve and 80-100% for a charge reserve.
In such nickel-metal hydride rechargeable batteries, allowing working forms of full charges and complete discharges, they are usually operated in the range of 0-100% of positive electrode capacity.
However, even in nickel-metal hydride rechargeable batteries having discharge and charge reserves at both end parts of the hydrogen-absorption capacity range of the hydrogen-absorption alloy, as mentioned above, the working forms of full charges and complete discharges result in deficiencies in the hydrogen-absorption alloy, such as a crack due to expansion at charging and corrosion due to repeated charge and discharge operations. These problems eventually lead to a shortened cycle life, which is expected to be overcome for prolonged battery life.